The present invention relates to a frequency controllable laser device. In particular, the invention relates to a frequency controllable laser device that is capable of being modulated or chirped at a high frequency.
Frequency chirped laser devices, for use in interferometry and the like, are known. In particular, it is known to provide laser devices that implement a so-called Littrow scheme in which the laser cavity includes a diffraction grating onto which collimated light is directed. Tilting of the diffraction grating permits the frequency and cavity length of the laser to be simultaneously altered to provide the required frequency tuning without mode hopping. The Littrow arrangement has, however, the disadvantage that the diffraction grating must be rotated about a well defined pivot point. The critically stable mechanical arrangement required to provide the necessary accuracy of grating motion thus makes it difficult to obtain high frequency modulation speeds.
U.S. Pat. No. 6,049,554 describes various examples of laser cavities based on the above mentioned Littrow scheme and the similar Littman scheme. In particular, U.S. Pat. No. 6,049,554 describes in detail how the pivot point for a diffraction grating or mirror can be mathematically derived to provide the synchronous change in laser frequency and cavity length that allows the output frequency to be changed without introducing unwanted mode hopping effects.